When a person with myopia develops presbyopia with age, he/she usually needs a separate pair of reading glasses or uses multi-focal lenses.
A conventional multi-focal lens such as a bifocal lens typically has multiple regions each having a different diopter. However, such a multi-focal lens has an optical aberration, and transition between the regions having different diopters is abrupt, which may make the wearer feel uncomfortable. In addition, since the diopter of each of the regions is fixed, it cannot be tuned according to the wearer's requirement.
U.S. Pat. No. 7,654,667 discloses a progressive addition lens operating in combination with a multi-order diffractive optic. It is disclosed therein an electro-active lens which has an electro-active diffractive addition region for making a diffractive addition region electro-active. The electro-active diffractive addition region includes two transparent electrodes, two alignment layers, an electro-active material, two electrical insulating layers, and drive electronics. The electro-active material may include, for example, a nematic liquid crystal or a cholesteric liquid crystal (CLC). However, since transparent electrodes are in the form of a common electrode, tuning of the diopter of the electro-active diffractive addition region is limited.
US 2015/0277151 discloses an optical device which includes an electro-optical layer, having an effective local index of refraction at any given location within an active area of the electro-optical layer that is determined by a voltage waveform applied across the electro-optical layer at the location. An array of excitation electrodes including parallel conductive stripes extending over the active area is disposed over one or both sides of the electro-optical layer. Control circuitry is coupled to apply respective control voltage waveforms to the excitation electrodes and is configured to concurrently modify the respective control voltage waveforms applied to excitation electrodes so as to generate a specified phase modulation profile in the electro-optical layer. Since the optical device is a passive matrix focusing device, the driving capability thereof for integrated circuits of high resolution products is limited and it is required to apply actuation voltage continuously.